The present invention relates to fluid systems and, more specifically, to determining change in fluid flow rate within a line.
In fluid management systems, a problem is the inability to rapidly detect an occlusion in a fluid line. If a patient is attached to a fluid dispensing machine, the fluid line may become bent or flattened and therefore occluded. This poses a problem since the patient may require a prescribed amount of fluid over a given amount of time and an occlusion, if not rapidly detected, can cause the rate of transport to be less than the necessary rate. One solution in the art, for determining if a line has become occluded, is volumetric measurement of the transported fluid. In some dialysis machines, volumetric measurements occur at pre-designated times to check if the patient has received the requisite amount of fluid. In this system, both the fill and delivery strokes of a pump are timed. This measurement system provides far from instantaneous feedback. If the volumetric measurement is different from the expected volume over the first time period, the system may cycle and re-measure the volume of fluid sent. In that case, at least one additional period must transpire before a determination can be made as to whether the line was actually occluded. Only after at least two timing cycles can an alarm go off declaring a line to be occluded.
A method for determining change in fluid flow rate within a line is disclosed. In accordance with one embodiment, the method requires applying a time varying amount of energy to a second fluid separated from the first fluid by a membrane. Pressure of the second fluid is then measured to determine a change in the first fluid""s flow rate, at least based on the pressure of the second fluid.
In another embodiment, the method consists of modulating a pressure of a second fluid separated from the first fluid by a membrane. The pressure of the second fluid is measured, and a value corresponding to the derivative of the pressure of the second fluid with respect to time is determined. The magnitude of the derivative value is then low pass filtered. The low pass output is compared to a threshold value for determining a change in the first fluid""s flow rate. In yet another embodiment, the method adds the steps of taking the difference between the pressure of the second fluid and a target value and varying an inlet valve in response to the difference between the pressure of the second fluid and the target value for changing the pressure of the second fluid toward the target value.
In another embodiment, the target value comprises a time varying component having an amplitude and it is superimposed on a DC component. The amplitude of the time varying component is less than the DC component.
In an embodiment in accordance with the invention, a fluid management system dispenses an amount of a first fluid and monitors a state of flow of the first fluid. The system has a chamber, an energy imparter, a transducer and a processor. The chamber has an inlet and an outlet and a septum separating the first fluid and a second fluid. The energy imparter applies a time varying amount of energy on the second fluid. The transducer is used for measuring a pressure of the second fluid within the chamber and creating a signal of the pressure. The processor is used for determining a change in the first fluid""s flow rate based on the signal.
In another embodiment, the fluid management system has the components of a chamber, a reservoir tank, a membrane, a transducer, and a processor. The reservoir tank contains a second fluid in fluid communication with the chamber and the tank has a valve disposed between the reservoir tank and the chamber. The membrane is disposed within the chamber between the first fluid and the second fluid and it is used for pumping the first fluid in response to a pressure differential between the first fluid and the second fluid. The transducer is used for measuring the pressure of the second fluid within the chamber and creating a pressure signal. The processor reads the pressure signal and takes the derivative of the pressure signal with respect to time. The processor then determines the magnitude of the derivative value and passes it through a low pass filter. The low pass output is then compared to a threshold value, for determining a change in the first fluid""s flow rate. A change in the first fluid""s flow rate causes an indicator signal. In another related embodiment, the processor controls the opening and closing of a valve in response to the difference between the pressure of the second fluid and a target value, the opening and closing of the valve adjusting the pressure of the second fluid toward the target value. In yet other embodiments, the first fluid may be dialysis fluid or blood and the second fluid may be air or a gas.